Many significant and commercially important uses of modern computer technology relate to images. These include image processing, image analysis and computer vision applications. The ability of a computer to correctly and accurately distinguish between a shadow and a material object within an image has been a persistent challenge to scientists. This is particularly important in connection with object recognition and tracking in motion image sequences. For example, a video camera fixed for observation of a field of view, for detection of the appearance and motion of certain objects of interest, can be coupled to a computer for analysis of the image sequence recorded by the camera. It is a reasonably straightforward task for the computer to distinguish background elements of the image (forming the unobstructed field of view) from changes in subsequent recorded images of the field of view. A difficulty is determining whether differences detected in subsequent image recordings are the result of moving objects, or are due to changes in the illumination flux radiating the field of view, for example, a shadow caused by the object.
If a cast shadow is indistinguishable from the object casting the shadow, it would not be possible for the computer to recognize the object. Thus, the ability of a computer to recognize a specific object moving within a preselected field of view being surveyed by a video camera is an important design consideration. Accordingly, there is a persistent need for the development of accurate and correct techniques that can be utilized in the operation of computers relating to images.